1. Field of the Invention
The present invention relates to a method of controlling the operation of large rotary machines such as steam turbines or generators while monitoring the vibrating state during the operation and especially at the time of starting.
The problem of vibration of rotary members occupies a great proportion of the maintenance time in operating thermal power stations, and the investigation of the causes and the countermeasures required to correctly grasp the situations require a detailed technical study. Further, the distance between the centers of the bearings, the weight of the rotors and the number of wheel chambers are on the increase accompanying the recent trend toward increased capacities of steam turbines, thereby causing the problem of vibration to become more complicated.
In regard to the control of power systems, on the other hand, it is also a modern trend to operate the thermal power plant to adjust the intermediate load while the base loads are being carried out by the nuclear power plant. The conventional weekly adjustment of load is now shifting toward the adjustment of load in daytime. Therefore, the machines of medium capacities in thermal stations are often stopped during such time zones as midnight in which the demand for power is small. In starting and stopping the operation of the plant, the abnormal condition tends to develop as compared with the case of steady-state operation. In starting the turbines particularly, the abnormal vibration tends to develop which is caused by the thermal unbalance.
In operating the steam turbines or generators, the operation staffs must pay their most careful attention at the time of starting the machines; the development of abnormal vibration during the starting presents a serious problem. Lack of proper treatment or the timing may result in a serious accident, particularly with the steam turbines which revolve at high speeds.
Even during the steady-state operation, any abnormal condition must be detected as early as possible and proper treatment must be effected in quickly so that it will not develop into a serious accident. The vibration during the steady-state operation also presents the same problem as that at the time of starting the operation.
According to the present invention, the normal or abnormal conditions of the rotary machines are monitored and discriminated, i.e., the states of the vibration signals are detected by vibration detectors which are installed, for example, on the bearings, and are monitored and discriminated, to thereby control the operation.
The present invention attained under such circumstances analyzes the detected vibration signals and stably controls the operation while locating the cause, in order to prevent any serious accident.
2. Description of the Prior Art
In starting the operation of a steam turbine, an apparatus for controlling the turbine speed operates a main steam valve or a by-pass valve responsive to a desired running speed of the turbine and a desired variation factor in running speed, so that the running speed is gradually increased.
In case vibration has developed during the speed-up, however, any one of the following three methods has so far been employed depending upon the amplitude of the vibration signals. The first method is to stop the speed-rising control by the speed-control apparatus and to switch the operation into a manual control so that the operation is controlled depending upon the discretion by the operating staffs. The second method is to maintain the running speed at a speed at which the vibration had developed, and not to effect the speed-rising control. The third method is to stop the turbine.
According to the first method, however, the control which is switched to the manual operation depends entirely upon the discretion of the operation staffs. Therefore, the persons skilled in this field of art are required. Further, the control of operation differs depending upon the individual staffs, and is not desirable.
According to the second method, there arises a problem of specific vibrating frequency during the running of rotary machines. Therefore, it is not necessarily desirable to maintain the running speed of the rotary machines at a speed at which the vibration is developed.
It has been known that the vibration increases in a critical speed region determined by the specific vibrating frequency of rotary machines consisting of turbines and generators directly coupled to the turbines. Accordingly, to maintain the running speed at a predetermined value as done by the abovementioned second method rather presents very dangerous conditions.
With the third method, on the other hand, the rotary members can be safely handled. The third method, however, is likely to effect unnecessary tripping. The vibration is caused by a variety of factors such as thermal unbalance, mechanical unbalance, state of a lubricating oil and running speed, and it is difficult to forecast the normal and abnormal conditions. Depending upon the cases, therefore, the vibration can be converged into a safe vibration region by maintaining the running speed of the rotary machines at a given value as accomplished by the abovementioned second method. Therefore, frequent use of the third method often results in unnecessary tripping. Conversely, if the standard for discretion is loosened to avoid the tripping, proper treatment may not often be effected under abnormal conditions.
What is important here is to determined whether it is safe to maintain the running speed thereby avoiding the tripping. Therefore, desirable effects will not be obtained unless it is determined in which speed region the rotary machine is rotating without maintaining the running speed in a dangerous region, and unless it is diagnosed what phenomenon is appearing as a cause of vibration.
Among the aforementioned causes of vibration, a countermeasure has been attempted in regard to the mechanical unbalance in order to minimize the development of vibration.
An example can be found, for instance, in J. W. Lund, J. Tonnesen: "Analysis and Experiments on Multi-Plane Balancing of a Flexible Rotor," ASME Paper No. 71-Vibr-74 (ASME Vibrations Conference, Tront, Canada, Sept. 8-10, 1971). This literature mentions to attain balance by detecting vibration in several places of a rotary machine, detecting the rotating speed, and calculating a correction weight by utilizing the method of least square. As for the method of measuring vibration, the literature schematically diagramatizes the instrumentation in FIG. 4, and gives the related description is a paragraph of "Instrumentation" (pp. 3 to 4).
Further, A. Clapis et al "Early Diagnosis of Dynamic Unbalances and of Misalignments in Large Turbogenerators", Energy Nuclear, Vol. 23/n. 5/maggio, 1976, pp. 271 to 277, discloses the measurement of dynamic unbalance and misalignment of axis of large turbine generators to apply it as an early diagnosis to cope with the troubles. This literature mentions two measuring methods, processing of signals for monitoring and early diagnosis, and relation between the amplitude and the phase caused by the unbalanced rotary members with reference to the rotating speed. Particularly, FIG. 2 of this literature shows a state for mounting the proximity transducers, and FIG. 3 shows a block diagram for processing the signals. According to this literature, the signals from the proximitors are subjected to the signal conversion through a predetermined BP filter. The literature, further, mentions to convert the vibration-phase signals or vibration signals of root mean square values into d-c components to record them.
Thus, according to most of the conventional arts, the vibration signals are smoothed and treated in the form of d-c components. According to such methods for treating the signals, however, a variety of factors are all diagnosed as a whole, making it difficult to effect fine diagnosis.
Further, F. H. Barratt et al., "ACTUS, An Automatically Controlled Turbine Run-up System", AEI Engineering, September/October, 1962, pp. 255-258, discloses a method that is practically applied to the operation for starting turbines.
This literature discusses the apparatus ACTUS that was developed by AEI, and mentions the speed-raising operation of turbines in a paragraph of "Problems of starting large steam turbine" on pages 255 to 256. This literature clearly mentions to raise the speed of the turbines while monitoring the misalignment of axis, vibration and temperature difference between the steam and the metals, which are out of the ordinarily specified ranges, as well as to maintain the speed no matter how fast or slowly the turbines may be running. This, however, is a method of controlling the running speed to a predetermined value under abnormal conditions as mentioned earlier, and is not necessarily advantageous.
In the foregoing were mentioned conventional arts for controlling the operation based on the results of the diagnosis of abnormal conditions, by way of (1) switching the controlling operation into manual controlling operation, (2) maintaining the running speed, and (3) tripping. The signals have been processed by way of smoothing, i.e., signals of average values or d-c signals have been brought into diagnosis.
The signals can be easily processed only if the signals of average values are employed. Thus the diagnosis is not possible unless the signals are converted into those of average values. That is, in case some particular frequency components are increased and other particular frequency components are decreased, the resulting decision will be that the state is not changed unless the average value is changed.
In practice, however, even when the average value is not changed, the increase of some particular frequency components will have to be often regarded seriously. Though the increases of such particular frequency components may not directly be related to the abnormal conditions, we know through experience that it is the beginning of abnormal conditions.
Consequently, when the vibration signals are diagnosed in the form of average values of the whole frequency components, it is difficult to correctly and faithfully diagnose the symptoms. The present invention is based on this fact, and makes it possible to safely control the operation of the turbogenerators, particularly at the time of starting the operation, based on a proper diagnosis which meets the practical demands.